Expression control and specificity of the basic amino acid exporter LysE of Corynebacterium glutamicum

LysE of Corynebacterium glutamicum belongs to a large new superfamily of tr anslocators whose members are probably all involved in the export of small solutes. Here, the transcript initiation site of lysE, and its divergently transcribed regulator gene, lysG, are identified. Single-copy transcription al fusions of lysE with lacZ, and titration experiments, show that LysG is the positive regulator of lysE expression enabling its up to 20-fold induct ion. This induction requires the presence of a coinducer, which is either i ntracellular L-lysine, or L-arginine. A competition experiment showed that LysE exports these two basic amino acids at comparable rates of about 0.75 nmol min(-1) (mg dry wt)(-1). Although L-histidine and L-citrulline also ac t as coinducers of lysE expression, these two amino acids are not exported by LysE. As is evident from the analysis of a lysEG deletion mutant, the ph ysiological role of the lysEC system is to prevent bacteriostasis due to el evated L-lysine or L-arginine concentrations that arise during growth in th e presence of peptides or in mutants possessing a deregulated biosynthesis pathway. C. glutamicum has additional export activities other than those of LysE for exporting L-histidine, L-citrulline and L-ornithine.